This application is a continuation-in-part application of co-pending U.S. patent application Ser. No. 08/962,024 filed Oct. 31, 1997.
1. Field of the Invention
This invention relates to an absorbent composite material which is particularly suitable for use in diapers, training pants, adult incontinence products, and the like. The absorbent composite material of this invention provides absorbent cores for such personal care absorbent articles having improved integrity, resistance to wet collapse, shape retention, and uptake rate. In addition, the material serves as a controlled rate retention material, exhibiting a controlled release swelling mechanism which is particularly suitable for diapers and other such personal care absorbent articles.
2. Description of Prior Art
Disposable absorbent articles such as diapers, training pants, adult incontinence garments, and the like have been known for some time. These products include an absorbent material which is used to absorb and hold or contain body fluids. Initially, in many of these products, the absorbent material comprised what is termed xe2x80x9cwaddingxe2x80x9d or plies of tissue. The wadding was disposed between a liquid-impermeable backing and a liquid-permeable facing and the plies of tissue were used to absorb and contain the liquid within the product.
Products using wadding-type absorbent materials were replaced, for the most part, by an improved absorbent material comprising xe2x80x9cfluffed wood pulp fibersxe2x80x9d. This absorbent material comprises a layer of individualized wood pulp fibers, with the layer having substantial thickness. This material provided personal care articles with the improved absorbent capacity and somewhat better containment than personal care articles using the wadding-type material. In addition, the fluffed wood pulp layer is quite soft, flexible, and conformable and, thus, produces an improved personal care article over personal care articles using wadding as the absorbent layer.
Although fluffed wood pulp absorbent materials provide improved capacity, the efficiency with which the capacity is used in personal care articles such as diapers is poor. This is due, in part, to the fact that the fluffed wood pulp absorbent material tends to break apart upon flexing and that once the absorbent material has accepted a substantial amount of liquid, the cellulosic fibers tend to collapse, sometimes causing liquid to be squeezed from the product and to leak. In addition, the fluid to be absorbed is generally deposited in a localized area and the ability of the fluid to move along the plane of the material is poor. U.S. Pat. No. 4,560,372 discloses an absorbent material of a layered structure for addressing these issues, the layered structure comprising a first fibrous layer substantially of resilient fibers and containing at least about 10% by weight of a superabsorbent material and a second layer of hydrophilic porous material substantially co-extensive with the first layer and superposed on the first layer.
Superabsorbents are polymers that are able to absorb fluid in quantities corresponding to many times their weight. They are also able to retain the absorbed fluid, even when subjected to external pressure. Such polymers have found wide use in absorbent personal care products such as diapers, sanitary pads and the like. These polymers are normally in particle form, such as in the form of grains, granules, flakes or fibers, and are typically layered or mixed with other absorbent materials, for example cellulose fibers.
The effectiveness of such superabsorbents in an absorbent material is contingent upon many factors including where and how the superabsorbent is incorporated into the absorbent material, its particle form and physical and chemical properties, and also the speed at which it absorbs fluids, its gel strength and its ability to retain absorbed fluids. One problem negatively affecting the absorbency of the absorbent material containing superabsorbents is that the superabsorbent particles located in a wetting region of the absorbent material bind the fluid in this region upon the first insult, thereby reducing the effectiveness of the material to absorb subsequent insults. As a result, the total absorption capacity of the absorbent body is not utilized to an optimal extent, thereby increasing the risk of fluid leakage from the article. This problem is even more acute where the articles are intended to be worn for extended periods of time, such as through the night during which wetting often occurs on several occasions.
Fluid distribution and material utilization are two critical performance measures for absorbent products such as diapers. It has been observed that the majority of soiled diapers exhibit uneven fluid distribution. Typically, the back portion of the diaper contains little or no absorbed fluid compared to the front/target area. As a result, there is severe under utilization of the absorbent material due to this inefficient fluid handling.
The movement of fluid away from the target zones requires the presence of two key functionalitiesxe2x80x941) fluid handling or xe2x80x9cdistributionxe2x80x9d throughout the entire product length and width and 2) xe2x80x9cslow absorptionxe2x80x9d retention material located in the target zone. The advantages of using delayed absorption superabsorbent materials in diapers is taught, for example, by British Patent Application GB-2-280-115-A. A slow absorbing retention material has the potential for higher absorbency rates while reducing product performance deterioration typically associated with later insults.
The Absorbency Time Index of a material is defined as:
Absorption Time Index=(t20+t40+t60+t80)/4
where ti is the time it takes for the material saturation to reach i% of the final (200 minute) value. Known superabsorbents such as STOCKHAUSEN FAVOR 836(copyright) and STOCKHAUSEN FAVOR 870(copyright), available from Stockhausen in Greensboro, N.C., and DOW DRY TECH 2035(copyright), available from Dow have very fast Absorption Time Indexes in the range of about 2.7 to about 4.0 minutes. STOCKHAUSEN FAVOR 836, STOCKHAUSEN FAVOR 870, and DOW DRYTECH 2035 are all water swellable, water insoluble, weakly crosslinked sodium polyacrylate polymers.
Samples based upon the teachings of U.S. Pat. No. 4,560,372 to Pieniak, UK Patent Application GB-2-280-115-A, and International Publication Number WO 91/10413 were prepared and evaluated with respect to Absorption Time Index of the disclosed materials. As shown in Table 1 hereinbelow, which summarizes the results obtained, the Absorption Time Index (ATI) for each of the disclosed materials was less than 2.6.
The materials used in the preparation of samples Code 1-4 were as follows:
Binderxe2x80x9435% solids ADCOTE 50T4990 available from Rohm and Haas Co.
SAPxe2x80x94FAVOR 880 available from Stockhausen
Fluffxe2x80x94NB416 available from Weyerhaeuser
Surfactantxe2x80x94Sodium dioctyl Sulfosuccinate 75.0% total solids from American Cynamid
The proportions thereof for each sample are shown in Table 2.
1. Spray PRIMACOR on air entrained fibers for 8 minutes
2. May add 1.74% surfactant based on PRIMACOR weight, but it is not necessary to do so
3. Mix SAP with wet coated fibers for 20 seconds
4. Deposit wet coated fibers+SAP in a loose pile and air dry at room temperature for 24 hours
Test each of sample Codes 1 and 2 disposed over each of sample Codes 3 and 4. Insert pads (Codes 1 and 2) are in vertical alignment with the dispersion pads (Codes 3 and 4) such that the insult liquid passes through the insert pads first.
Binder fibers used to produce these samples were polypropylene type PF015 made by Montell USA. The wetting agent was MASIL SF-19 made by PPG Industries. The amount added was 2.0% by total weight PF015 and MASIL SF-19. Fluff pulp was CR-1654 made by US Alliance Coosa, and the superabsorbent was FAVOR 880 by Stockhausen.
Samples were prepared by taking a nonwoven material comprising polyester and bicomponent fiber with a void volume of 10 cc/g @0.01 psi and a basis weight of less than about 150 gsm and distributing 50% by weight superabsorbent, e.g. FAVOR 880, onto one surface based upon weight of the nonwoven material. A layer of tissue having a surface area equal to that of the nonwoven material was weighed out and placed over the surface of the nonwoven material containing the largest amount of superabsorbent. 10 to 50% moisture based on the combined weight of the nonwoven material, superabsorbent and tissue was added and the resulting layered structure compressed under a load of 200 to 500 psi. Machine direction rows of 0.5xe2x80x3 slits spaced 0.25xe2x80x3 apart were applied after which the sample was pulled in the cross direction to open up the slits to provide the apertures.
It is one object of this invention to provide an absorbent composite material suitable for use in personal care absorbent products, such as diapers, training pants, adult incontinence garments, and the like, having improved integrity, resistance to wet collapse, shape retention, and uptake rate.
It is another object of this invention to provide an absorbent composite material having the capability of serving as a controlled rate retention material.
It is yet another object of this invention to provide an absorbent composite material having the capability of slowing down the absorption rate of superabsorbents which normally have inherently high absorption rates.
It is another object of this invention to provide an absorbent composite material having an Absorption Time Index greater than the Absorption Time Index of known materials.
These and other objects of this invention are achieved by an absorbent composite material having an Absorption Time Index greater than about 10 minutes comprising a fibrous absorbent material selected from the group consisting of fluff pulp, synthetic fibers, natural fibers, and combinations thereof, a superabsorbent material having a superabsorbent Absorption Time Index of less than about 5 minutes, and a binding agent, the binding agent binding at least a portion of the fibers of the fibrous absorbent material. The fibrous absorbent material comprises in the range of about 10% to about 90% by weight of the absorbent composite material and the superabsorbent material comprises in the range of about 10% to about 90% by weight of the absorbent composite material. The binding agent is preferably a tacky adhesive or tacky polymeric fibers.